The ancient Maya had what was arguably the most advanced civilization in the Americas. For instance, they made dramatic breakthroughs in astronomy that helped them very accurately predict where the moon and other planets would be in the sky centuries in the future. They also left behind many books and stone inscriptions regarding the stories of their gods and the history of their divine kings and queens.

For unknown reasons, the ancient Mayan civilization then disintegrated more than a millennium ago. The number of people declined catastrophically to a fraction of the empire's former size, and the ruins of its great cities are now largely overgrown by jungle. [Photos: First Glimpse into a Mayan Tomb]